1. Field of the Invention
This invention relates to digital transmission systems and, more particularly, to digital transmission by asynchronous message switching on a common time-divided transmission loop.
2. Description of the Prior Art
It is often desirable to exchange digital information between digital machines. If such machines are separated by any significant geographic distance, it has heretofore been necessary to either purchase or lease a dedicated transmission facility between such machines, or to arrange a temporary connection between such machines by means of common carrier, switched transmission facilities. Since it is the nature of digital machines to require large amounts of digital channel capacity, but only for brief periods and only occasionally, the heretofore available facilities described above have proven very inefficient for this use. Dedicated transmission facilities, for example, remain unused the vast majority of the time. Switched, common carrier facilities tend to be restricted in bandwidth to voice frequencies and hence are not immediately adaptable to high speed digital transmission.
A further problem with switched facilities is the fact that it often takes more time to set up the transmission path than is required for the entire transmission of data. The telephone network requires real time transmission in the sense that signals must be delivered substantially at the same time they are generated. It therefore is standard procedure to set up the communication path in its entirety before any signals are transmitted. As a result, centralized switching has been used in the telephone plant. Digital transmission of data, on the other hand, need not be done in real time and hence it is wasteful to set up an entire connection prior to transmission. These facts tend to make presently available interconnection facilities uneconomical for intermachine digital communications.
It is therefore an object of the present invention to provide improved digital transmission between digital machines.
It is another object of the present invention to allow digital machines having widely varying data handling capabilities to communicate efficiently and ecomonically.
It is a further object of this invention to provide a system which allows a digital machine to communicate with a plurality of other digital machines without the need for reprogramming that machine when the number or capabilities of machines in the system is changed.
It is a still further object of this invention to provide an algorithm which takes advantage of the inherent characteristics of digital machines to provide a more efficient method of using transmission resources.